Insulating first floor suspended floors - do I need membranes?

[lizziecupcakes]

Hi all,
I am getting ready to insulate my ground floor suspended floors using historic england’s guide. I am just waiting for it to warm up a bit more before we get cracking.

This will involve using a draught-proof membrane, some natural insulation (eg hemp or sheep’s wool), and then the top layer will be the water vapour permeable membrane to prevent condensation.

In the meantime, me and my partner are wondering if anyone has insulated their first floor suspended flooring e.g an upstairs bedroom, hallway? The electricians we had pulled up a few boards in each bedroom and it looks like we could fairly easily roll some insulation under them and we thought now would be the time to do it, since we will want to sanding the floors soon.

I am not sure if insulating bedroom and upstairs hallway floors is advised? Is it worth it? Also, is insulation alone enough because I imagine I know I won’t need the draught-proof membrane but will I need the water vapour membrane layer at all?

I just wasn’t sure about the later

Thank you

 

[fernicarry]

Vapour membrane is to stop water vapour generated by living in the building from getting into the fabric of the building. In the case of a first floor then you have vapour generating activities i.e. people, on both sides of it so no point.

Personally I'm not completely convinced you should use it at all unless you are completely wrapping the whole of the shell as per a new build. The water vapour is still going to be generated internally and still has to find somewhere to go so if you prevent it leaving through the floor structure it may find somewhere less benign to collect in. No evidence to support this I just think its best to interfere in the movement of water vapour as little as possible when remediating.

If you have airflow between the ceiling and the floor then a breather membrane might be worth it. This place is ventilated behind the plaster and that air moves quite readily along between the first floor joists so for that reason I do put down a membrane when I get the opportunity. I was fitting some downlightrs in the downstairs hallway recently and was shocked at the amount of air coming out of the hole.

The bigger benefit from the insulation will be acoustic which might be appreciated if you have bare floorboards. Standard practice here is to put a layer of ash and sand in between the joists to act as sound deadening -- which is as filthy as it sounds whenever you need to work on the ceiling below, but works extremely well. I shudder to think how many tons of extra loading it puts on the joists...

 

[lizziecupcakes]

Thanks @fernicarry . I think that makes sense. So, for our first floor, I’ll just stick to the insulation only. I am hoping it will help with warmth and acoustics

 

[alexander]

you can buy acoustic insulation, just don't fill the space up to the gunnels allow for a little air movement you will create a condensation issue

 

[CliffordPope]

Ground floor or first floor?

 

[lizziecupcakes]

First floor - bedrooms. That’s the suspended flooring area I want to insulate.

I want the bedrooms to feel nice and cozy over winter.

This past winter had been unbearable

 

[paulc]

In the meantime, me and my partner are wondering if anyone has insulated their first floor suspended flooring e.g an upstairs bedroom, hallway? The electricians we had pulled up a few boards in each bedroom and it looks like we could fairly easily roll some insulation under them and we thought now would be the time to do it, since we will want to sanding the floors soon.

I am not sure if insulating bedroom and upstairs hallway floors is advised? Is it worth it?

Yes, I have added insulation in the void between ceiling & floor in a couple of bedrooms so can answer a couple of your questions.
Has it made the bedrooms any warmer (or the rooms below) - Not that I can detect or measure.
Has it reduced the amount of noise being heard from above/below - Again, no. If anything, noise levels may be worse as a result of using laminate flooring in the bedrooms.
Was it worth the effort - Nah.

That said, I used fibreglass which is non-combustible. So for the box room over the kitchen, the insulation will slow the spread of fire should the unthinkable ever happen.

 

[lizziecupcakes]

Yes, I have added insulation in the void between ceiling & floor in a couple of bedrooms so can answer a couple of your questions.
Has it made the bedrooms any warmer (or the rooms below) - Not that I can detect or measure.
Has it reduced the amount of noise being heard from above/below - Again, no. If anything, noise levels may be worse as a result of using laminate flooring in the bedrooms.
Was it worth the effort - Nah.

That said, I used fibreglass which is non-combustible. So for the box room over the kitchen, the insulation will slow the spread of fire should the unthinkable ever happen.

Thanks @paulc . I’m really surprised you didn’t notice any heat insulation benefits.
Just wondering if your ground floor suspended floors are insulated though? If not, do you think doing it would make a difference to upstairs/first floor with insulation?

thank you for sharing

 

[Ashville87]

I don’t think you’ll get much heat benefit from insulating the first floor joists if there’s a heated room below. Heat rises so enough loft insulation above is more beneficial but I’m sure I read you’ve sorted that. If the bedroom was unbearable this winter have you got a draughty window or an undersized radiator maybe?

 

[lizziecupcakes]

If the bedroom was unbearable this winter have you got a draughty window or an undersized radiator maybe?

i think it’s mainly coming the non-insulated draughty suspended floors from the ground floor. All this cold kept coming in and the upstairs was a bit warmer thanks to the loft insulation, but I generally felt really uncomfortable on a daily basis unless the heating was on. We bought electric throws in the end which have been amazing! But I do think it would have been worse had we not done the loft insulation, thankfully we did although it took ages.

I am reconsidering the insulation now. My partner thinks we could experiment though, with just one bedroom and see how that goes.

I think it’s going to take a few years to really get a feel for this house and it’s character, but I generally dread winter and need to get this place warmer before the next

 

[paulc]

Thanks @paulc . I’m really surprised you didn’t notice any heat insulation benefits.
Just wondering if your ground floor suspended floors are insulated though? If not, do you think doing it would make a difference to upstairs/first floor with insulation?

Insulation only really works if one side is colder than the other. So if your ground floor rooms are heated to say 20°C, and the bedrooms are at 18°C, there is going to be very little transfer of heat between the two. The greater the difference in temperatures, the bigger the transfer of heat.
Unfortunately for me, insulating the ground floor is difficult - Have tongue & groove floorboards which are very difficult to lift without damage (would also need to remove skirting to get them up). The joists are weedy little 3x2 affairs resting on stumpy dwarf walls. Limited to how much insulation could be fitted without compromising ventilation in the void. Also have an uninsulated concrete slab in the kitchen extension. No way am I digging that thing up... Instead, I have used 5mm thick woodfibre laminate underlay over the top of the floorboards & concrete. Whilst it doesn't provide much in the way of insulation, it has stopped a lot of the cold draughts.

 

[lizziecupcakes]

I have used 5mm thick woodfibre laminate underlay over the top of the floorboards & concrete. Whilst it doesn't provide much in the way of insulation, it has stopped a lot of the cold draughts.

yes! It’s the draughts! I bet that makes all the difference to you.

I don’t even mind killing off the draughts on my ground floor and forgoe the insulation. I just want (need) the cold to stop coming in. Since I am (sadly) taking up most floorboards, I might as well add the insulation

I’m looking for a good Victorian/edwardian floorboards reclaimation yard in the meantime (in the south London area), but if I have to, I will just have to get new treated pine floorboards and hope they blend in enough with the old floorboards once sanded.

I don’t mind leaving my own mark on the house

 

[paulc]

I don’t even mind killing off the draughts on my ground floor and forgoe the insulation. I just want (need) the cold to stop coming in. Since I am (sadly) taking up most floorboards, I might as well add the insulation

With most of the boards up, you may as well put in some insulation. Personally, I'd go for a PIR/PUR rigid board cut to be a snug fit between the joists. Use a few battens to keep the boards in place, and fill any gaps with expanding foam. Or if you want to go for natural materials, a woodfibre board. Which ever material you decide to go for, limit the thickness to 50% of the joist depth over any dwarf walls.

 

[lizziecupcakes]

Thanks @paulc . I’ll explore these options too. With respect to the PIR/PUR rigid board method (or woodfibre), do you mean add this and then lay the insulation over this, then over that add a water vapour (breathable) membrane? Would PIR/PUR rigid board (or woodfibre boards) help with draught? (I’d definitely invest in the woodfibre boards)

We are happy to do all this slowly and gathering advice and suggestions as we go. We don’t mind it being a slow process with the first ground floor living room; just waiting for the weather to warm up before we get down and dirty!

 

[lizziecupcakes]

Btw I’ve been using this resource from historic England:

https://historicengland.org.uk/images-books/publications/eehb-insulation-suspended-timber-floors/heag086-suspended-timber-floors/

 

[paulc]

With respect to the PIR/PUR rigid board method (or woodfibre), do you mean add this and then lay the insulation over this, then over that add a water vapour (breathable) membrane? Would PIR/PUR rigid board (or woodfibre boards) help with draught? (I’d definitely invest in the woodfibre boards)

See image below...
With PIR/PUR boards, the foil facing will act as a vapour barrier, so no need for any additional membranes. If you went for woodfibre boards, I'm not convinced that any membrane is needed.

 

[lizziecupcakes]

Thanks @paulc that’s a really helpful photo. So, in your method, you don’t add insulation at all, you’re just using battens to hold the PIR/PUR board up, and then replace the floorboards? Sorry for the clarification; it just seems the joists are quite short so insulation wouldn’t fit in there (in that specific photo).

 

[paulc]

Building Regulations require a u-value of 0.25 W/m²K in refurbishments. However, if it is not technically possible, one should do the best possible within space and budget constraints.
The joists in that image appear to be 4"x3", so 50mm high battens supporting 50mm PIR/PUR board is about as much as will fit in the available space without compromising airflow. Whilst not reaching the specified u-value, 50mm would fall within the "best possible", and better than none.